.TH std::unordered_map::at 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::unordered_map::at \- std::unordered_map::at

.SH Synopsis
   T& at( const Key& key );             \fB(1)\fP \fI(since C++11)\fP
   const T& at( const Key& key ) const; \fB(2)\fP \fI(since C++11)\fP
   template< class K >                  \fB(3)\fP (since C++26)
   T& at( const K& x );
   template< class K >                  \fB(4)\fP (since C++26)
   const T& at( const K& x ) const;

   Returns a reference to the mapped value of the element with specified key. If no
   such element exists, an exception of type std::out_of_range is thrown.

   1,2) The key is equivalent to key.
   3,4) The key compares equivalent to the value x. The reference to the mapped value
   is obtained as if by expression this->find(x)->second.
   The expression this->find(x) must be well-formed and have well-defined behavior,
   otherwise the behavior is undefined.
   These overloads participate in overload resolution only if Hash::is_transparent and
   KeyEqual::is_transparent are valid and each denotes a type. This assumes that such
   Hash is callable with both K and Key type, and that the KeyEqual is transparent,
   which, together, allows calling this function without constructing an instance of
   Key.

.SH Parameters

   key - the key of the element to find
   x   - a value of any type that can be transparently compared with a key

.SH Return value

   A reference to the mapped value of the requested element.

.SH Exceptions

   1,2) std::out_of_range if the container does not have an element with the specified
   key.
   3,4) std::out_of_range if the container does not have the specified element, that
   is, if find(x) == end() is true.

.SH Complexity

   Average case: constant, worst case: linear in size.

.SH Notes

                Feature-test macro                Value    Std          Feature
                                                                 Heterogeneous
                                                                 overloads for the
                                                                 remaining member
   __cpp_lib_associative_heterogeneous_insertion 202311L (C++26) functions in ordered
                                                                 and unordered
                                                                 associative
                                                                 containers. (3,4)

.SH Example

    This section is incomplete
    Reason: no example

.SH See also

   operator[] access or insert specified element
              \fI(public member function)\fP

.SH Category:
     * Todo no example
